Effects of S-methoprene on growth, development, and reproduction of Acyrthosiphon pisum.

As an analogue of juvenile hormone, S-methoprene regulates the development, metamorphosis, and reproduction of insects by interfering with the normal metaboilic level of juvenile hormone in insects, and thus has been widely used as a biochemical insecticide. To clarify the effects of S-methoprene on the growth, development, and reproduction of Acyrthosiphon pisum, we measured the survival rate, developmental duration, adult body size, body weight, longevity, fecundity and reproductive system of A. pisum under different concentrations (0, 50, 100, 500, 1000 mg·L-1) of S-methoprene by plant mediation in vitro. The results showed that S-methoprene treatment did not affect the survival rate and developmental duration of A. pisum, but had significant effects on body size, adult longevity and fecundity of A. pisum adult. With the increases of S-methoprene concentration, the proportion of sterile adult increased significantly, adult body size and weight decreased gradually, and the adult longevity and reproductive period shortened gradually. The average fecundity of per female and the average daily fecundity per female gradually decreased. At the concentration of 1000 mg·L-1 S-methoprene, adult body weight (2.41 mg) was 1.30 mg lower than that of the control, and body length (3.74 mm), body width (1.34 mm), hind food tibia length (2.68 mm) and surface area (3.95 mm2) were 12.4%, 15.7%, 11.3% and 26.1% lower than those of the control. The number of sterile adult accounted for 50.9%, and the adult longevity (14.3 d) and reproductive period of A. pisum (12.2 d) were the shortest. The average fecundity of per female (83.5 ind) and the average daily fecundity of per female (6.8 ind·d-1) were the lowest. Under S-methoprene treatments, the number of newly deve-loped embryos in the ovary of A. pisum adults significantly decreased, and the number of mature embryos with eye spots increased gradually and the appendages such as antennae and feet of mature embryos became more obvious, but the size of the first embryo was significantly reduced. The results showed that S-methoprene shortened adult longevity and decreased fecundity, and significantly inhibited the new embryo production and embryo size in the ovarian tubes of A. pisum. This study would provide a theoretical basis for the potential value of juvenile hormone analogues in regulating aphid population.